CODEWITHSUNDEEP
objective-cc-preprocessor
The Tosters
The Tosters

Reputation: 417

Concat two macros in Objective-C

I'm trying to concatenate two values each defined as macro. At this moment I've:

#define VAL1 @"im/"
#define VAL2 @"test"
#define GLUE_IN(x,y) (x ## y)
#define GLUE(x,y) GLUE_IN(x,y)

when I use it in code:

[array addObject:GLUE(VAL1, VAL2)];

it produces me an error: Pasting formed '"im/"@', an invalid preprocessing token

I'm aware that it may be solved by:

#define GLUE(x,y) [NSString stringWithFormat:@"%@%@",x,y]

however I'm curious is it possible to achieve this same result using preprocessor?

Upvotes: 0

Views: 1195

Answers (2)

Stas
Stas

Reputation: 641

I'm not gonna ask why you ever need it, but here is possible solution:

#define VAL1 im
#define VAL2 test
#define STR2(x) #x
#define STR(x) STR2(x)
#define GLUE_IN(a,b) a##b
#define GLUE(x,y) GLUE_IN(x,y)

…

NSString *val1 = @(STR(GLUE(VAL1, VAL2)));
NSString *val2 = @"another " @"test";
NSLog(@"%@, %@", val1, val2);

It gives you

imtest, anothertest

However, you'll have some troubles with a slash sign. If I were you, I'd prefer another way.

Upvotes: 0

Joachim Isaksson
Joachim Isaksson

Reputation: 180917

## concatenates tokens, not strings, which causes an invalid resulting token, and in this case is entirely un-necessary since @"im/" @"test" - being compile time string constants - will be appended anyway. Just do;

#define GLUE_IN(x,y) (x y)

...which will result in 

[array addObject:@"im/" @"test"]

...and things should work well.

Upvotes: 2

Related Questions